1. Technical Field
The present invention relates to the field of imaging and ranging system, and, more particularly, to stereo imaging at daytime, nighttime and harsh weather conditions by active gated imaging.
2. Discussion of Related Art
Stereo imaging is widely used by automotive manufactures for Advance Driver Assistance Systems (ADAS) functions such as night vision support, traffic sign recognition, object recognition lane recognition and the like. Stereo imaging provides two main advantages versus a single camera: at least two different scene imagery (i.e. captured by the cameras in different location in the vehicle and each camera may have different electro-optical characteristics such as Field-of-View, sensitivity etc.) and the second is three-dimensional information (i.e. ranging capabilities, stereoscopy) by triangulation.
European Patent No. EP 1,831,718 B1, titled “stereo camera for a motor vehicle” describes a device based on at least two cameras being different from each other with respect to at least one property such as light sensitivity, pixel dimensions, color filter array etc. Furthermore, the aforementioned device implements ADAS functions such as night vision support and/or traffic sign recognition and/or object recognition and/or road boundary recognition and/or lane recognition and the like. However, the aforementioned device does not address several important aspects such as the need for a dedicated Near-IR (NIR) light source for night vision support, does not address motor vehicle external installation and not addressing backscattering due to vehicle light source (e.g. front headlamps, night vision support NIR light source etc.) interaction with particles in the atmosphere such as rain, snow, hail etc. Furthermore, the aforementioned device does not simplify installation requirements of the cameras (required for three-dimensional information, e.g., by triangulation).
Accuracy of passive stereoscopy (i.e. three-dimensional information based on triangulation) depth information may be estimated by Eq. (1).
                              Δ          ⁢                                          ⁢          d                =                                            d              2                                      l              ·              h                                ⁢          Δ          ⁢                                          ⁢          x                                    (        1        )            
Whereas Δd is the depth information estimation, d is the depth, l is the length of the baseline (i.e. distance between the cameras), h is the distance between the image plane and the plane through the centers of the central projection of the two cameras and Δx is the disparity (i.e. sum of distances from for each camera center to a projected specific point in the viewed scenery). This depth information estimation limits every passive stereoscopy based system, namely at longer viewed distances and when baseline is limited to short lengths.